In recent years, functions of portable digital equipment, such as compact thin digital AV players and digital cameras, have been enhanced, and therefore, there is a growing need for large-capacity high-speed nonvolatile memory elements used as memory elements of the above equipment. To meet the need, a nonvolatile memory element using a ferroelectric capacitor is available.
Many of ferroelectric layers are made of an oxide. Therefore, such memory materials need to be manufactured by a manufacturing process which does not expose the memory materials to a reduction atmosphere, such as a hydrogen atmosphere, and the nonvolatile memory element having an element structure which can be manufactured in such manufacturing process is required.
Generally, in a final step of the manufacturing process of a semiconductor element in which MOS transistors are integrated, the MOS transistors damaged by, for example, sputtering are subjected to a heat treatment in a gas containing hydrogen to restore the characteristics of the MOS transistors. Moreover, in a manufacturing process of the nonvolatile memory element using the ferroelectric, the surface of a semiconductor substrate on which the semiconductor element is manufactured is covered with an interlayer insulating layer, such as a BPSG layer, a PSG layer, or the like. However, it is known that in the case of forming such interlayer insulating layer, hydrogen is generated as a product.
To prevent the ferroelectric layer to be exposed to hydrogen generated in such manufacturing process, one example is that in a semiconductor memory apparatus using the ferroelectric capacitor, the ferroelectric layer is entirely covered with an insulating hydrogen barrier layer. However, the insulating hydrogen barrier layer is not electrically conductive. Therefore, a contact hole is formed on the insulating hydrogen barrier layer for electrical connection to penetrate therethrough, and a hydrogen barrier material, such as TiN, having both the electrical conductivity and the hydrogen barrier property is embedded in the contact hole using CVD. Thus, an upper electrode of the ferroelectric capacitor and a wire on the insulating hydrogen barrier layer are electrically connected to each other, and the ferroelectric layer is protected by the insulating hydrogen barrier layer and the hydrogen barrier material embedded in the contact hole without being exposed to hydrogen (see Patent Document 1 for example).
Moreover, there is another example in which the upper electrode and a lower electrode sandwiching the ferroelectric layer are entirely covered with the hydrogen barrier layer, or only the upper electrode is covered with the hydrogen barrier layer, and the connections between the ferroelectric capacitor and other circuit elements, wires, etc. are realized by drop contact using a plug (see Patent Documents 2 and 3 for example).
Moreover, there is still another example in which a layer, such as a TaSiN layer, which maintains an amorphous state even if a heat treatment for crystallizing the ferroelectric layer is carried out is formed as a hydrogen barrier layer on or above the capacitor constituted by the ferroelectric layer. The TaSiN layer has an excellent effect of blocking hydrogen and has electrical conductivity. Therefore, without forming a hole on the hydrogen barrier layer, the upper electrode of the capacitor and an external electrode can be electrically connected to each other by the TaSiN layer (see Patent Document 4 for example).
Moreover, the nonvolatile memory element using not the ferroelectric but the resistance variable layer as the memory material is known (see Patent Document 5 for example).
Patent Document 1: Japanese Laid-Open Patent Application Publication 2002-151659
Patent Document 2: Japanese Laid-Open Patent Application Publication 2005-39299
Patent Document 3: Japanese Laid-Open Patent Application Publication 2006-66934
Patent Document 4: Japanese Laid-Open Patent Application Publication Hei 11-126883
Patent Document 5: Japanese Laid-Open Patent Application Publication 2004-185755